Congenital blindness interferes with optimal human development by severely restricting the range and variety of opportunities for learning about space. Lacking visual input, the developing blind child must rely on his remaining senses to first gather information about his envrionment's spatial layout, then construct an adequate representation of that layout and finally to formulate strategies for effectively reasoning about spatial relationships. Presumably, all this activity is critical to independent orientation and mobility, as defined by the safe and successful negotiation of a pre-planned, novel route of travel. Formal instruction of blind children is in part intended to foster the acquisition of concepts which enable the child to move through and understand his physical environment. Difficulties arise because the blind child cannot easily monitor his progress by continually updating his position in space relative to stable perceptual landmarks in any way comparable to the sighted child. This study attempts to demonstrate that blind children can learn to localize objects in space utilizing auditory information provided by a new generation sonar sensory aid -- the Trisensor. In addition, it will he determined whether training on the Trisensor results in improved performance on spatial concept measures, including measures of the advanced abilities mental rotation and changing perspective. A battery of spatial concept assessments will be administered to eight congenitally totally blind school age children prior to training. Training with the Trisensor to localize objects will occur for twenty hours over a ten week period. The battery of spatial concept assessments will be readministered to assess the effects of training. A second, advanced Trisensor training phase , directly emphasizing change of perspective, will be conducted for six hours over a three week period. Finally the assessment battery will be administered. The results of this training and assessment will determine the usability of the Trisensor for near space activities, the extent to which Trisensor training generalizes to non Trisensor spatial tasks, and whether the Trisensor improves performance on complex spatial tasks.